The study was a single-site, double-blind, randomized, placebo-controlled, parallel group study to evaluate the efficacy of adjunctive ramelteon in the treatment of insomnia and mood stability in patients with euthymic bipolar disorder for up to 24 weeks of maintenance treatment. Participants with euthymic bipolar disorder and sleep disturbances were randomized to receive adjunctive ramelteon or placebo in addition to their reular psychiatric medications for up to 24 weeks or until they experienced a relapse (defined as a depressed or manic event).